How do I apply textures to imported .obj?
Since you have Blender Internal selected, I'll assume you want to use GLSL shading.

To see textures in the viewport, first select GLSL shading, and make sure the viewport is set to textured mode.



Now, In order to have a texture, your object first needs a material. Add one, and name it whatever you want. (When I did it before, I named it "paint" - but the material name isn't important.



Now that you have a material, you'll need to add a texture to that material. Add a texture on that material, and then open your image for that texture.



I added some better lighting to the scene, and already it is working.



(In this case, the OBJ already had a UV map - all I had to do was use the default unwrap option, to use the map already with the OBJ)

But lets say that you wanted to also add an emissive texture, to create glowing bits. In this case, I'm using a black and white texture, and it can be simply layered on top.

On your same material as before, add a new texture (just as with the first one). Add your emissive texture as the image, and there will only be one setting that you need to change to make it work: change the blend mode from "mix" to "screen." 



Instead of being all black (except the white bits), this texture should layer on top of the first texture, with the white parts displaying properly.